• Title/Summary/Keyword: Crack Tip

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A Fatigue Behavior for Spot Welded Steel Plate Carbon C by the Variation of the Interval Between Two Spots (냉간압연강판 접용접재의 너깃간의 거리에 따른 피로거동)

  • Song, Sam-Hong;Yang, Yun-Jin;Jeon, Jae-Uk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.11
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    • pp.2845-2852
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    • 2000
  • When welding a car frame with one spot welding there are same limitations because many parts of it cannot be simplified by one spot welding alone. It is presented two spot welding model for the description of the spot welding which is usually used in a car frame structure. This study primarily covers fatigue behavior taking spot welded SPCC(Steel plate carbon C) with different ungget intervals as a tension shear specimen. It was prepared that intervals between two nuggets are varied as 9mm, 14mm, and 20mm respectively. The tensile tests and fatigue tests were executed to know the mechanical properties under static and fatigue load condition. In addition, the relationship between fatigue life and nugget intervals was illustrated by finite element method.

Comparative Study on Crack Tip Opening Displacment ${\delta}_5$ R-Curve and ${\delta}_{BS}$ R-Curve (균열선단 열림변위 {\delta}_5 R-곡선과 {\delta}_{BS} R-곡선의 비교연구)

  • Kim, Eom-Gi;Nam, Seung-Hun;Jin, Uk;Go, Seong-Wi
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.3 s.174
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    • pp.794-802
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    • 2000
  • Since the examination of CTOD problem revealed that the discrepancy among CTOD's was a matte., of definition, the relationships among parameters based on different definitions have been studied Particularly, the relationship between $\sigma$BS R-curve based on BS 7448 and R-curve based on the recently introduced $\sigma$5 parameter was investigated in this research. For the comparison, compact tension specimens of used 1Cr-0.5Mo steel, heat treated 1Cr-0.5Mo steel to mimic the new one, A12024-T6, and A12024-T351 were prepared and tested. Consequently, the relationship between $\sigma$5 and $\sigma$BS R-curves for tested materials were established by shifting the rotational center which could determined by rotation factor and ligament size.

Model for predicting tool life of diamond abrasive micro-drills during micro-drilling of ceramic green bodies (세라믹 성형체의 미소구멍 가공 시 다이아몬드 입자 전착 드릴의 공구 수명 예측 모델)

  • 이학구;이대길
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2003.06a
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    • pp.593-598
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    • 2003
  • Ceramic plates containing many micro-holes are used in diverse applications such as MCP (Microchannel Plate). catalytic converters, filters, electrical insulators in integrated circuits, and so on. One of the efficient methods for machining many holes in ceramic plates is wet drilling of ceramic green bodies followed by sintering them. Since the strength of ceramic green bodies is much lower than the strength of sintered ceramic plate, ceramic green bodies can be drilled with high feed rate. The axial force during micro-drilling of ceramic green bodies increases rapidly at high feed rate, which induces the crack in workpiece. Therefore, the tool lift of micro-drill with respect to feed rate may be determined by the predicting increase of axial force. In this work, the axial force during micro-drilling was calculated using the chip flow model on the micro-drill tip. from which the tool life of diamond abrasive micro-drill during micro-drilling of ceramic green bodies was calculated.

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Root Cause Analysis on the Steam Turbine Blade Damage of the Combined Cycle Power Plant (복합화력발전소 증기터빈 동익 손상 원인분석)

  • Kang, M.S.;Kim, K.Y.;Yun, W.N.;Lee, W.K.
    • Journal of Power System Engineering
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    • v.12 no.4
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    • pp.57-63
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    • 2008
  • The last stage blade of the low pressure steam turbine remarkably affects turbine plant performance and availability Turbine manufacturers are continuously developing the low pressure last stage blades using the latest technology in order to achieve higher reliability and improved efficiency. They tend to lengthen the last stage blade and apply shrouds at the blades to enhance turbine efficiency. The long blades increase the blade tip circumferential speed and water droplet erosion at shroud is anticipated. Parts of integral shrouds of the last stage 40 inch blades were cracked and liberated recently in a combined cycle power plant. In order to analyze the root cause of the last stage blades shroud cracks, we investigated operational history, heat balance diagram, damaged blades shape, fractured surface of damaged blades, microstructure examination and design data, etc. Root causes were analyzed as the improper material and design of the blade. Notches induced by erosion and blade shroud were failed eventually by high cycle fatigue. This paper describes the root cause analysis and countermeasures for the steam turbine last stage blade shroud cracks of the combined cycle power plant.

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A Study on the Cold Formability of Drawn Dual-Phase Steels (신선 가공된 이상 조직강의 냉간 성형성에 대한 연구)

  • 박경수;최상우;이덕락;이종수
    • Transactions of Materials Processing
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    • v.13 no.1
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    • pp.84-89
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    • 2004
  • There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment. However, Non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, Dual-Phase Steels were studied as candidate materials for non-heat treated steels, which have different martensite morphologies and volume fractions obtained through heat-treatment of intercritical quenching (IcQ), intermediate quenching (ImQ) and step quenching (SQ). The mechanical properties of DP steels were measured by tension and compression tests. Also, the cold formability of three DP steels which have similar tensile strength value was investigated by estimating the deformation resistance and the forming limit. The deformation resistance which is important factor in determining die life was estimated by calculating the deformation energy. And the forming limit was estimated by measuring the critical strain revealing crack initiation at the notch tip of the specimens.

Impact fracture behavior on particle volume fraction of nano silica composite materials (입자 함유율의 변화에 따른 나노 실리카 복합재료의 충격파괴거동)

  • LEE, Jung-Kyu;KOH, Sung Wi
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.51 no.3
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    • pp.454-460
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    • 2015
  • The present study is undertaken to evaluate the effect of volume fraction on the results of Charpy impact test for the rubber matrix filled with nano sized silica particles composites. The Charpy impact tests are conducted in the temperature range $0^{\circ}C$ and $-10^{\circ}C$. The range of volume fraction of silica particles tested are between 11% to 25%. The critical energy release rate $G_{IC}$ of the rubber matrix composites filled with nano sized silica particles is affected by silica volume fraction and it is shown that the value of $G_{IC}$ decreases as volume fraction increases. In regions close to the initial crack tip, fracture processes such as matrix deformation, silica particle debonding and delamination, and/or pull out between particles and matrix which is ascertained by SEM photographs of Charpy impact fracture surfaces.

Impact Fracture Behaviors of Zr-Based Bulk Amorphous Metals (Zr-기 벌크 아몰퍼스 금속의 충격 파괴 거동)

  • Ko, Dong-Kyun;Jeong, Young-Jin;Shin, Hyung-Seop;Oh, Sang-Yeob
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.1246-1251
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    • 2003
  • The fracture behaviors of Zr-based bulk amorphous metals(BAMs) having compositions of $Zr_{55}Al_{10}Ni_{5}Cu_{30}$, were investigated under impact loading and quasi-static conditions. For experiments, a newly devised instrumented impact testing apparatus and the subsize Charpy specimens were used. The influences of loading rate and the notch shape on the fracture behavior of the Zr-based BAM were examined. The Zr-based BAMs showed an elastic deformation behavior without any plastic deformation on it before fracture. Most fracture energies were absorbed in the process of the crack initiation. The maximum load and fracture absorbed energy under quasi-static condition were larger than those under impact condition. However, there existed relatively insignificant notch shape effect. Fracture surfaces under impact loading were smoother than those under quasi-static loading. The absorbed fracture energy appeared differently depending on the extent of the vein-like pattern region due to the shear bands developed at the notch tip. It can be found that the fracture energy of the Zr-Al-Ni-Cu alloy is closely related with the development of shear bands during fracture.

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Characteristics of GMA Weld Zone on TiO2 Different Component Flux Cored Wire for S500 Grade Steel (TiO2 성분 플럭스충진와이어에 따른 S500강의 GMA 용접부 특성)

  • Yoo, Cheol;Ko, Young-Bong;Park, Kyeung-Chae
    • Journal of the Korean institute of surface engineering
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    • v.48 no.6
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    • pp.335-342
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    • 2015
  • Recently, the production of oil and gas at the arctic ocean and offshore has been growing. Accordingly, S500 steel with the high tensile strength and excellent toughness has been used and flux cored wire that can be welded to the S500 has been required. In this study, we carried out observation of microstructures, mechanical properties and CTOD (crack tip openning displacement) in the weld zone that GMA (gas metal arc) welded with different component of $TiO_2$ flux core wire (the main components, rutile or Ti-slag) for S500 steel. Weld zone produced with Ti-slag flux cored wire has formed a enough acicular ferrite and shown excellent impact toughness at $-40^{\circ}C$, tensile strength at room temperature and CTOD at $-20^{\circ}C$. As a result, the developed flux cored wire was suitable for S500 steel.

Failure analysis of prestressing steel wires

  • Toribio, J.;Valiente, A.
    • Steel and Composite Structures
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    • v.1 no.4
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    • pp.411-426
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    • 2001
  • This paper treats the failure analysis of prestressing steel wires with different kinds of localised damage in the form of a surface defect (crack or notch) or as a mechanical action (transverse loads). From the microscopical point of view, the micromechanisms of fracture are shear dimples (associated with localised plasticity) in the case of the transverse loads and cleavage-like (related to a weakest-link fracture micromechanism) in the case of cracked wires. In the notched geometries the microscopic modes of fracture range from the ductile micro-void coalescence to the brittle cleavage, depending on the stress triaxiality in the vicinity of the notch tip. From the macroscopical point of view, fracture criteria are proposed as design criteria in damage tolerance analyses. The transverse load situation is solved by using an upper bound theorem of limit analysis in plasticity. The case of the cracked wire may be treated using fracture criteria in the framework of linear elastic fracture mechanics on the basis of a previous finite element computation of the stress intensity factor in the cracked cylinder. Notched geometries require the use of elastic-plastic fracture mechanics and numerical analysis of the stress-strain state at the failure situation. A fracture criterion is formulated on the basis of the critical value of the effective or equivalent stress in the Von Mises sense.

Development of Elastic-Plastic Fracture Analysis Program for Structural Elements under an Impact Loadings (충격하중을 받는 구조부재의 탄소성 파괴해석 프로그램 개발)

  • K.S. Kim;J.B. Park
    • Journal of the Society of Naval Architects of Korea
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    • v.35 no.1
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    • pp.61-71
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    • 1998
  • This paper describes a dynamic fracture behaviors of structural elements under elastic or elasto-plastic stress waves in two dimensional space. The governing equation of this problem has the type of hyperbolic partial differential equation, which consists of the equation of motions and incremental elasto-plastic constitutive equations. To solve this problem we introduce Zwas' method which is based on the finite difference method. Additionally, in order to deal with the dynamic behavior of elasto-plastic problems, an elasto-plastic loading path in the stress space is proposed to model the plastic yield phenomenon. Based on the result of this computation, the dynamic stress intensity factor at the crack tip of an elastic material is calculated, and the time history of a plastic zone of a elasto-plastic material is to be shown.

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